1. Field of Invention
The present invention relates to a Wireless Local Area Network (WLAN) (e.g. defined in the IEEE 802.11 Protocol Specification). Specifically, the present invention refers to the standardization of solutions for interworking between WLAN and other networks (namely the third Generation Partnership Project (3GPP), 3GPP2 and IEEE 802.16 (related to Broadband Wireless Access)). The present invention refers also to the Media Independent Handoff (MIH) solutions being defined in the IEEE 802.21 Protocol Specification.
2. Problem in the art
FIG. 1 shows, by way of example, typical parts of an IEEE 802.11 WLAN system, which is known in the art and provides for communications between communications equipment such as mobile and secondary devices including personal digital assistants (PDAs), laptops and printers, etc. The WLAN system may be connected to a wireless LAN system that allows wireless devices to access information and files on a file server or other suitable device or connecting to the Internet. The devices can communicate directly with each other in the absence of a base station in a so-called “ad-hoc” network, or they can communicate through a base station, called an access point (AP) in IEEE 802.11 terminology, with distributed services through the AP using local distributed services set (DSS) or wide area extended services (ESS), as shown. In a WLAN system, end user access devices are known as stations (STAs), which are transceivers (transmitters/receivers) that convert radio signals into digital signals that can be routed to and from communications device and connect the communications equipment to access points (APs) that receive and distribute data packets to other devices and/or networks. The STAs may take various forms ranging from wireless network interface card (NIC) adapters coupled to devices to integrated radio modules that are part of the devices, as well as an external adapter (USB), a PCMCIA card or a USB Dongle (self contained), which are all known in the art.
FIGS. 2a and 2b show diagrams of the Universal Mobile Telecommunications System (UMTS) packet network architecture, which is also known in the art. In FIG. 2a, the UMTS packet network architecture includes the major architectural elements of user equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and core network (CN). The UE is interfaced to the UTRAN over a radio (Uu) interface, while the UTRAN interfaces to the core network (CN) over a (wired) Iu interface. FIG. 2b shows some further details of the architecture, particularly the UTRAN, which includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). In operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to GSM base stations. Each Node B may be in radio contact with multiple UEs via the radio interface (Uu) shown in FIG. 2a. A given UE may be in radio contact with multiple Node Bs even if one or more of the Node Bs are connected to different RNCs. For instance, a UE1 in FIG. 2a may be in radio contact with Node B2 of RNS1 and Node B3 of RNS2 where Node B2 and Node B3 are neighboring Node Bs. The RNCs of different RNSs may be connected by an Iur interface which allows mobile UEs to stay in contact with both RNCs while traversing from a cell belonging to a Node B of one RNC to a cell belonging to a Node B of another RNC. One of the RNCs will typically act as the “serving” or “controlling” RNC (SRNC or CRNC), while the other RNC will act as a “drift” RNC (DRNC). The mobile UEs are able to traverse the neighboring cells without having to re-establish a connection with a new Node B because either the Node Bs are connected to a same RNC or, if they are connected to different RNCs, the RNCs are connected to each other. During such movements of the mobile UE, it is sometimes required that radio links be added and abandoned in a handover situation so that the UE can always maintain at least one radio link to the UTRAN.
The interworking of the WLAN (IEEE 802.11) shown in FIG. 1 with other technologies (e.g. 3GPP, 3GPP2 or 802.16) such as that shown in FIGS. 2a and 2b is being defined at present in protocol specifications for 3GPP and 3GPP2. In IEEE protocol specification, such activities are carried out in IEEE 802.11 TGu and in IEEE 802.21 (the latter specification focusing specifically on the handoff of a device).
The interworking of these two types of networks or technologies can be split in two different scenarios:                Roaming: In such case, the STA connects to a new WLAN network, such as that shown in FIG. 1; and        Handoff: In such case, the same issues apply, but are more pressing since mobility must take place with minimal delay.        
The interworking implies several aspects, but one of the major issues identified is network selection. Specifically, due to the current standards, the STA known in the art can discover very little about a WLAN network before authenticating and associating, where authentication is understood to be the process of determining the identity of a user accessing a system, and where association is understood to be the process of registering with a system or network to allow information to be transmitted and received with a device or system. In operation, a beacon signal is periodically transmitted (broadcast) from devices to identify their device and/or network to allow devices to determine which radio coverage area and device they are communicating with. However, the beacon signal and/or the content of Probe Response messages provide limited information, e.g.:                Both during roaming and handoff, the STA cannot discover whether the required connectivity is supported, e.g. IPv4 versus IPv6, connectivity to the Internet, type of protocols supported (e.g.), etc. (see document [1] below);        Both during roaming and handoff, identifying whether a certain WLAN network enables an STA to roam based on its belonging to a given operator is rather cumbersome (e.g. the STA must store a long list of Service Set Identities (SSIDs), and the list must be kept updated frequently); and        During handoff, it is essential for the STA to know whether it is entering a new domain and if the handoff entitles only an L2 handoff or requires a L3 handoff as well. Current solutions have shown to be inefficient and produce considerable delays. Some solutions have been proposed (see documents [3], [4] below).        
Besides the interworking with other networks, availability of additional information to an STA regarding a certain network is needed in other scenarios. One example is mesh IEEE 802.11 networks, where different mechanisms for routing and security may be supported, the mesh network may or may not have connectivity to the Internet (i.e. “grounded” mesh versus “freestanding” mesh), and there can be other characteristics the STA needs to know before deciding whether or not to connect to the mesh network, and how to do so and what mechanisms to use.
In the past, several attempts took place to add new information to the WLAN beacon. The size of the beacon and the frequency at which it is sent impacts considerably the system capacity. Adding too much information to the beacon can be damaging (due to impact on the system capacity) and it would not be accepted easily in IEEE 802.11. Specifically, previous proposals that tried to create a new beacon information/type (see document [2]) were met with low acceptance in IEEE. Therefore modifications should be kept at a minimum. This implies that one cannot add all the information actually required to the beacon and let STAs discovery them by listening to the beacon.
The reader is referred to the following documents, which are hereby incorporated by reference in their entirety herein:
[1] “Network Characteristics for AP Selection”, documents IEEE 802.11-05/1595r0 and IEEE 802.11-05/1594r0, Airespace;
[2] “Adaptive Beaconing”, document 802.11-02/601r0, Nokia
[3] “Domain Identification for predictive handover among different domains”, Samsung, IEEE 802.11-04/711r0;
[4] “Access Router Identifier (ARID) for supporting L3 mobility”, Samsung, IEEE 802.11-04/710r0 [3] and [4] advocates that, when an handover takes place, the terminal needs to know whether it is moving between different domains (e.g. admin domains/security domains) and if a L3 handoff is needed (e.g. due to change of subnet) to speed up the detection of this. Specifically, document [4] advocates adding to the 802.11 beacon the AIRD (i.e. Access Router Identity) to allow the terminal to detect the change of subnet. It is believed this would not be efficient nor work in all cases, consistent with that provided in document [5] below; and
[5] patent application Ser. No. 10/196,457 (NC17212/NC17213), by Stefano Faccin, describes a mechanism to enable optimized delivery of information to a terminal over a wireless link. Specifically, the idea therein is to avoid sending the whole IP Router Advertisement to the wireless terminals at the actual frequency it is generated by an Access Router. Instead, a functionality in the wireless point of attachment (e.g. the Access Point (AP) in WLAN or an access controller for WLAN) forwards to the terminals over L2 (e.g. the beacon in 802.11) only a subset of information (e.g. the subnet prefix) to allow the terminal to detect whether an L3 handover is implied when changing e.g. the access point (AP).